U.S. patent application number 12/014511 was filed with the patent office on 2009-07-16 for metal gate electrode stabilization by alloying.
This patent application is currently assigned to International Business Machines Corporation. Invention is credited to Veeraraghavan S. Basker, Hariklia Deligianni, Rajarao Jammy, Vamsi K. Paruchuri, Lubomyr T. Romankiw.
Application Number | 20090179279 12/014511 |
Document ID | / |
Family ID | 40849902 |
Filed Date | 2009-07-16 |
United States Patent
Application |
20090179279 |
Kind Code |
A1 |
Basker; Veeraraghavan S. ;
et al. |
July 16, 2009 |
METAL GATE ELECTRODE STABILIZATION BY ALLOYING
Abstract
Stabilized metal gate electrode for complementary
metal-oxide-semiconductor ("CMOS") applications and methods of
making the stabilized metal gate electrodes are disclosed.
Specifically, the metal gate electrodes are stabilized by alloying
wherein the alloy comprises a metal selected from the group
consisting of Re, Ru, Pt, Rh, Ni, Al and combinations thereof and
an element selected from the group consisting of W, V, Ti, Ta and
combinations thereof.
Inventors: |
Basker; Veeraraghavan S.;
(Yorktown Heights, NY) ; Deligianni; Hariklia;
(Tenafly, NJ) ; Jammy; Rajarao; (Hopewell
Junction, NY) ; Paruchuri; Vamsi K.; (New York,
NY) ; Romankiw; Lubomyr T.; (Briarcliff Manor,
NY) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ LLP
1875 EYE STREET, N.W., SUITE 1100
WASHINGTON
DC
20006
US
|
Assignee: |
International Business Machines
Corporation
Armonk
NY
|
Family ID: |
40849902 |
Appl. No.: |
12/014511 |
Filed: |
January 15, 2008 |
Current U.S.
Class: |
257/407 ;
205/238; 205/261; 257/E21.159; 257/E29.139; 438/585 |
Current CPC
Class: |
H01L 21/28079 20130101;
H01L 29/495 20130101; H01L 29/4966 20130101; H01L 29/517 20130101;
H01L 21/28176 20130101; C25D 3/567 20130101; C25D 5/02 20130101;
C25D 7/12 20130101; H01L 21/28088 20130101 |
Class at
Publication: |
257/407 ;
438/585; 205/261; 205/238; 257/E21.159; 257/E29.139 |
International
Class: |
H01L 21/283 20060101
H01L021/283; H01L 29/43 20060101 H01L029/43; C25D 3/00 20060101
C25D003/00 |
Claims
1. A metal gate electrode comprising a metal selected from the
group consisting of Re, Ru, Pt, Rh and combinations thereof and an
alloying compound selected from the group consisting of Ni, Y, Ti,
Ta, W, C, Al and combinations thereof.
2. The metal gate electrode of claim 1 having a work-function
greater than or equal to the metal or combination of metals wherein
the work-function is calculated by the following formula .phi. m =
4.6 + V FB .+-. kT ln ( N a n i ) ##EQU00004## such that, V.sub.FB
is the flat band voltage of the metal; kT is 0.0259 eV;
n.sub.i=1.45.times.10.sup.10; and N.sub.a is the doping density of
the silicon substrate.
3. The metal gate electrode of claim 1 wherein the alloying
compound is present at about 0.1% to about 10% by weight.
4. The metal gate electrode of claim 1 wherein the alloying
compound is W at a concentration from about 4% to about 9% by
weight.
5. The metal gate electrode of claim 1 wherein the alloying
compound is Ni at a concentration from about 0.1% to about 2.5% by
weight.
6. The metal gate electrode of claim 1 wherein the alloying
compound is carbon at a concentration from about 2% to about 6.5%
by weight.
7. A bath for electrochemically depositing a metal and alloying
compound onto a substrate comprising a strong acid and a metal or
metal salt selected from the group consisting of Re, Ru, Pt, Rh and
combinations thereof and an alloying compound selected from the
group consisting of Ni, Y, Ti, Ta, W, C, Al and combinations
thereof wherein the alloying compound has a bath concentration of
about 1 g/L to about 500 g/L of alloying compound.
8. The bath of claim 7 wherein the alloying compound is W having a
bath concentration from about 1 g/L to about 50 g/L.
9. The bath of claim 8 wherein the bath further comprises from
about 1 g/L to about 50 g/L of sodium citrate.
10. The bath of claim 7 wherein the alloying compound is Ni having
a bath concentration from about 1 g/L to about 50 g/L.
11. The barn of claim 7 wherein the alloying compound is C having a
bath concentration of sodium citrate from about 5 g/L to about 500
g/L.
12. A methods of making a stabilized metal gate electrodes
comprising the steps of forming a metal gate electrode pattern
comprising a metal selected from the group consisting of Re, Ru,
Pt, Rh, and combinations thereof and an alloying compound selected
from the group consisting of Ni, Y, Ti, Ta, W, C, Al, and
combinations thereof; and subjecting the metal gate electrode
pattern to a forming gas anneal.
13. The method of claim 12 wherein the metal gate electrode has a
work-function greater than or equal to the metal or combination of
metals wherein the work-function is calculated by the following
formula .phi. m = 4.6 + V FB .+-. kT ln ( N a n i ) ##EQU00005##
such that, V.sub.FB is the fiat band voltage of the metal or
combination of metals; kT is 0.0259 eV;
n.sub.i=1.45.times.10.sup.10; and N.sub.a is the doping density of
the silicon substrate.
14. The method of claim 12 wherein the alloying compound of the
formed metal gate electrode is present at about 0.1% to about 10%
by weight.
15. The method of claim 12 wherein the alloying compound of the
formed metal gate electrode is W at a concentration of about 4% to
about 9% by weight.
16. The method of claim 12 wherein the alloying compound of the
formed metal gate electrode is Ni at a concentration of about 0.1%
to about 2.5% by weight.
17. The method of claim 12 wherein the alloying compound of the
formed metal gate electrode is C at a concentration of about 2% to
about 6.5% by weight.
18. The method of claim 12 wherein the alloying compound is W and
the metal gate electrode pattern is formed by electrodeposition in
a bath comprising about 1 g/L to about 50 g/L of a W salt.
19. The method of claim 12 wherein the alloying compound is Ni and
the metal gate electrode pattern is formed by electrodeposition in
a bath comprising about 1 g/L to about 100 g/L of a Ni salt.
20. The method of claim 12 wherein the alloying compound is C and
the metal gate electrode pattern is formed by electrodeposition in
a bath comprising about 1 g/L to about 500 g/L of sodium citrate.
Description
TECHNICAL FIELD
[0001] The present disclosure relates generally to the
stabilization of metal gate electrodes. In particular, it relates
to a stabilized metal gate electrode by alloying for complementary
metal-oxide-semiconductor ("CMOS") applications and methods of
making the stabilized metal gate electrodes.
BACKGROUND
[0002] A common trend in modern integrated circuit manufacturing is
to produce transistors having very small feature sizes. For
competitive high density integrated circuits, features such as the
conductors, source and drain junctions, and interconnections to the
junctions must be made as small as possible. As feature sizes
decrease, the sizes of the resulting transistors and the
interconnections between transistors also decrease. Smaller
transistors allow more transistors to fit on a single substrate.
Furthermore, smaller transistors usually have lower turn on
threshold voltages and taster switching speeds and consume less
power in their operation. These features allow for higher speed
integrated circuits.
[0003] As semiconductor transistors become smaller, a number of
problems have arisen. For instance, use of a very thin gate
dielectric causes high gate current leakage, which diminishes
device performance. Also, a higher doping level is needed in the
channel to reduce short channel effect in order to ensure that the
transistor properly turns off. Using a very high concentration of
dopant in the channel decreases current drive and can lead to
undesirable drain-to-channel tunneling current.
[0004] Polysilicon gate technology, which is often employed,
carries with it additional problems. For example, polysilicon gates
tend to suffer from polysilicon depletion or boron penetration
effects, causing poor performance. Additionally, a polysilicon gate
has a fixed work function determined by a certain high level of
doping.
[0005] Metal is another material used for gate electrodes. Metal
has a variety of advantages over polysilicon as a gate electrode
material. For example, metal allows for excellent current flow and
has less voltage depletion problems than polysilicon. Metal too,
however, has its own drawbacks. Some metals, like Ti and Ni, are
highly diffusive and act as contaminants within the channel region,
particularly during the high temperature conditions required for
dopant activation of the source/drain implant. Also, certain work
functions are required that allow transistors to work optimally,
and it is more difficult to manipulate the work function of metals
than it is to manipulate the work function of polysilicon.
Moreover, metals are difficult to etch properly. Dry-etch methods
are too harsh on underlying Si substrates while wet-etch methods
can excessively undercut the sidewalls of the gate electrode.
[0006] Methods to solve some of these problems have been attempted
by combining the conventional methods of forming the transistor
with polysilicon as the gate electrode during doping with the
additional steps of completely etching out the polysilicon after
doping and replacing it with a metal. This replacement process,
however, is complex and can often result in costly errors if not
done properly.
BRIEF SUMMARY OF THE DISCLOSURE
[0007] The present disclosure is drawn to the stabilization of
metal gate electrodes by alloying for complementary
metal-oxide-semiconductor ("CMOS") applications and methods of
making the stabilized metal gate electrodes. Modern silicon CMOS
transistors require the use of metal gate electrodes with high-k
dielectrics such as HfO.sub.2. These electrodes must be
electrically stable and able to withstand the high temperatures
required during manufacturing. The present disclosure is drawn to a
field-effect transistor having a gate electrode comprising a metal
selected from the group consisting of Re, Ru, Pt, Rh, Ni, Al and
combinations thereof and an element selected from the group
consisting of W, V, Ti, Ta and combinations thereof.
[0008] Typically, the metal gate electrode has a work-function
greater than or equal to the metal or combination of metals wherein
the work-function is calculated by the following formula
.phi. m = 4.6 + V FB .+-. kT ln ( N a n i ) ##EQU00001##
[0009] such that,
[0010] V.sub.FB is the flat band voltage of the metal;
[0011] kT is 0.0259 eV;
[0012] n.sub.i=1.45.times.10.sup.10;
[0013] and N.sub.a is the doping density of the silicon
substrate.
[0014] Besides a Si substrate, any semiconductor substrate may be
used including SiGe, Ge or GaAs with appropriate adjustments to the
above formula for the work-function.
[0015] The metal gate electrodes typically comprise an alloying
compound or combination of alloying compounds present in an amount
of 0.1% to about 25%, about 0.1% to about 15%, or about 0.1% to
about 10% by weight. In one embodiment the alloying compound of the
metal gate electrodes is W at a concentration of about 4% to about
9% by weight, or the alloying compound of the metal gate electrodes
is Ni at a concentration of about 0.1% to about 2.5% by weight, or
the alloying compound of the metal gate electrodes is C at a
concentration of about 2% to about 6.5% by weight.
[0016] The present disclosure is also drawn to methods of making a
stabilized metal gate electrode comprising the steps of forming a
metal gate electrode pattern comprising a metal selected from the
group consisting of Re, Ru, Pt, Rh, and combinations thereof and an
alloying compound selected from the group consisting of Ni, Y, Ti,
Ta, W, C, Al, and combinations thereof; and subjecting the metal
gate electrode pattern to a forming gas anneal. The forming gas
provides an environment for forming alloys and can also serve to
passivate the dielectric layer on the metal gate electrode.
Typically, the forming gas anneal is conducted at a temperature of
about 300.degree. C. to about 1000.degree. C., of at a temperature
of about 450.degree. C. to about 650.degree. C.
[0017] In one embodiment, the method is drawn to making a metal
gate electrode having a work-function greater than or equal to the
metal or combination of metals wherein the work-function is
calculated by the following formula
.phi. m = 4.6 + V FB .+-. kT ln ( N a n i ) ##EQU00002##
[0018] such that,
[0019] V.sub.FB is the fiat band voltage of the metal or
combination of metals;
[0020] kT is 0.0259 eV;
[0021] n.sub.i=1.45.times.10.sup.10;
[0022] and N.sub.a is the doping density of the silicon
substrate.
[0023] Typically, the metal gate electrodes are formed in baths
used for electrochemically depositing the metal and the alloying
compound onto a substrate. The baths provide small quantities of
alloying compounds, which stabilize the electrical properties of
the gate metal while not adversely affecting its work-function. For
instance, the alloying compound W may be deposited onto a wafer in
a bath comprising from about 1 g/L to about 50 g/L, or from about 1
g/L to about 20 g/L of a W salt. Examples of W salts include Sodium
tungstate and Ammonium tungstate. Additionally, the bath may
further comprise from about 1 to about 50 g/L of sodium citrate.
The alloying compound Ni may be deposited onto a wafer in a bath
comprising from about 1 g/L to about 50 g/L, or from about 1 to
about 20 g/L of a Ni salt. Examples of Ni salts include Nickel
sulfate, Nickel chloride or Nickel sulfamate. The alloying compound
C may be deposited onto a wafer in a bath comprising from about 5
g/L to about 500 g/L or from about 25 g/L to about 100 g/L of
sodium citrate. Furthermore, the baths used for electrochemically
depositing the metal and the alloying compound onto a substrate may
optionally include a strong acid, such as hydrochloric acid, in
concentrations from about 1 mL/L to about 100 mL/L or about 1 mL/L
to about 50 mL/L or about 5 mL/L to about 25 mL/L.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 shows the electrochemical curves obtained by various
rhenium alloy deposition baths.
[0025] FIG. 2 shows the Micro Rutherford back scattering analysis
of Re, Re--C, and Re--W.
[0026] FIG. 3 shows the capacitance-voltage characteristics of
electrodeposited Re and Re alloys.
[0027] FIG. 4a presents the capacitance-voltage curves of Re as a
function of temperature.
[0028] FIG. 4b presents the capacitance-voltage curves of Re--W
alloy as a function of temperature.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0029] The present disclosure is drawn to field-effect transistors
having a gate electrode comprising a metal selected, from the group
consisting of Re, Ru, Pt, Rh, Ni, Al and combinations thereof and
an element selected from the group consisting of W, V, Ti, Ta and
combinations thereof.
[0030] FIG. 1 gives the electrochemical curves obtained by various
rhenium alloy deposition baths. The curves were obtained by
sweeping the potential cathodically with respect to an open circuit
potential. The substrate used was a blanket p-Si/10 .ANG. chemox/30
.ANG. HfO.sub.2 substrate. Since light is typically used to
generate electrons in the case of p-Si, all curves were obtained
under illumination. White composite light was used for this
purpose. Since electrons are generated by light, the limiting
currents seen in all the baths under high overpotentials are
determined by the intensity of the incident light. The figure shows
that the Re-alloys all have higher activation potentials than Re
alone.
[0031] FIG. 2 shows the Micro Rutherford back scattering ("RBS")
analysis of the various alloys which spectroscopically confirms the
presence of the various elements. The RBS analysis also detects the
presence of Hf, which is present as part of the HfO.sub.2 layer
below the deposited layer of metal/metal alloy film. These spectra
allow quantitative amounts of each element of the deposited film to
be calculated, which are shown in Table 2.
[0032] FIG. 3 shows the capacitance-voltage characteristics of
electrodeposited Re and Re alloys on a bulk p-Si/10 .ANG.
SiO.sub.2/30 .ANG. HfO.sub.2 stack MOS test structures (100
.mu.m.times.100 .mu.m). The measurements were made after the
samples were exposed to a 550.degree. C. forming gas anneal for 30
minutes. For comparison, another sample was plated with Re (not an
alloy of Re). The Re sample was also fabricated on p-Si/10 .ANG.
SiO.sub.2/30 .ANG. HfO.sub.2.
[0033] Plotting CV curves of Re and comparing them to the CV curves
of the Re-alloys allows one to determine whether the alloy can
successfully be used as a metal gate electrode. Elements and/or
alloys that destroy the electrical characteristics of the base
metal are not typically used as a metal gate electrode.
[0034] To evaluate the effect of alloying on the electrical
properties of Re, capacitance-voltage characteristics of the alloy
films were obtained. The CV curves were used to calculate the
work-function of a metal gate electrode by measuring the flat band
voltage (V.sub.FB) of the metal. Once V.sub.FB is determined, the
work-function of the metal .phi..sub.m can be calculated by the
following formula:
.phi. m = 4.6 + V FB .+-. kT ln ( N a n i ) ##EQU00003##
[0035] where kT=0.0259 eV, n.sub.i=1.45.times.10.sup.10 and N.sub.a
is the doping density of the silicon substrate used for die test.
For p-Si, the kT sign is positive and n-Si, it is negative. The
work function of electrodeposited Re was 5.2 eV. If, for example,
an alloy shifted the work-function to 4.6 eV (the mid-gap of Si
transistors), then that alloy could not be used as a metal gate
electrode. The CV curves of Re-citrate, Re--W and Re--Ni all have
work-functions greater than or equal to 5.2 eV. The work function
of Re is 5.15 eV. The work function for Re--C is 5.25 eV. The work
function for Re--W and Re--Ni is 5.30 eV and 5.50 eV
respectively.
[0036] FIGS. 4a and 4b compare the electrical properties of
electrodeposited Re and Re--W alloy as a function of annealing
temperature. Typically, Re metal electrodeposited using a backside
contact scheme shows band edge work-function (5.2 eV) for use as
metal gate electrode. However, when the metal gate stack is
annealed at higher temperature, the work-function shifts as shown
in FIG. 4a. Hence, Re is alloyed with W in order to stabilize its
electrical properties. FIG. 4b shows that Re alloyed with W exhibit
stable work-function even after exposing it to 1000.degree. C.
annealing. The Re--W alloy did not have a protective cap layer of
TiN). However, work-function of Re metal shifts towards midgap even
when protected with a cap layer of TIN. This result shows that
Re--W exhibit more stable properties than Re metal alone.
[0037] The metal gate electrodes of the present invention typically
comprise an alloying compound or combination of alloying compounds
present in an amount of 0.1% to about 25%, about 0.1% to about 15%,
or about 0.1% to about 10% by weight. In one embodiment the
alloying compound of the metal gate electrodes is W at a
concentration of about 4% to about 9% by weight, or the alloying
compound of the metal gate electrodes is Ni at a concentration of
about 0.1% to about 2.5% by weight, or the alloying compound of the
metal gate electrodes is C at a concentration of about 2% to about
6.5% by weight.
[0038] The present disclosure provides methods of making a
stabilized metal gate electrodes comprising the steps of forming a
metal gate el